Asphalts combined with aggregates have been employed as paving compositions for many years. Asphalts generally include bitumens as a predominant constituent and are conventionally obtained as a solid residue from the distillation of crude petroleum. In forming paving compositions, asphalts must be converted to a fluid state.
One fluid form of asphalt is the suspension or emulsion of asphalt in water. After spreading and compressing aggregate/asphalt emulsion paving compositions, the water evaporates and the asphalt hardens into a continuous mass. Another fluid form of asphalt employed in paving is a cutback, i.e., a fluid petroleum product produced by fluxing an asphaltic base with a suitable organic solvent or distillate. Pavements are formed by spreading aggregate/cutback paving compositions and evaporating the volatile distillate from the mass.
An advantage of forming pavements with asphalt emulsions and cutbacks is the avoidance of high temperature application. In the most common paving technique, the asphalt and aggregate are mixed and applied at elevated temperatures in order to maintain the asphalt in a fluid state in forming the pavement. This asphalt, which is neither cutback nor emulsified, is referred to as an asphalt cement.
A major problem with cutbacks and emulsions is their low adhesivity to aggregate in comparison to asphalt cement. This is due primarily to the presence on the aggregate surface of (a) the organic solvent or oil in the cutback and (b) the water in the emulsion which interfere with the formation of an adhesive bond between the aggregate and the asphalt.
One technique which has been disclosed to increase the adhesivity of emulsions and cutbacks is set forth in U.S. Pat. No. 3,243,311. There, the aggregate is pretreated with one of a variety of metal compounds stated to be cross-linking agents for the organic binder to oxidize, polymerize or catalyze and thereby harden the binder. The pretreatment is supposed to improve adhesivity of the binder and aggregate, specifically for clay-type soil aggregates. The cross-linking agents are stated to be multioxidation state metals in their higher oxidation state, with the anions including a large variety of organic and inorganic acids. In addition, salts such as the halides and a large variety of inorganic oxides are mentioned. The cations disclosed include Group I, Group IV, Group V, Group VII, and Group VIII metals as well as rare earth metals. Specific examples include Cu(OH).sub.2, CuCl.sub.2, FeCl.sub.3, CuSO.sub.4 and KMnO.sub.4. In each instance, the soil is pretreated with the cross-linking agent prior to mixing with the asphalt.
In U.S. Pat. No. 1,328,310, an asphaltic pavement is disclosed in which copper sulfate is added to the asphalt for improving physical properties. Other compounds mentioned for this purpose include the sulfates or selenates of aluminum, chromium, iron, indium, gallium, and the sulfates or selenides of sodium, potassium, rubidium, ammonium, silver, gold, platinum or thallium. These compounds are relatively insoluble in the asphalt.
In U.S. Pat. No. 2,773,777, a bituminous composition particularly suitable for airport runways exposed to the high temperatures of the exhaust gases of jet engines is disclosed. The composition includes bitumen emulsion, portland cement, and mineral aggregate. To this mixture is added an aqueous solution of one of a number of water soluble salts for the purpose of giving plasticity to the composition. The salts disclosed are water-soluble polyvalent metal salts of a strong mineral acid, especially sulfuric, hydrochloric and/or phosphoric acids. The most effective salts are stated to be alkali earth metal salts including calcium chloride, magnesium chloride, barium chloride and the like. Salts of amphoteric metals are also taught to be useful, including aluminum sulfate, chromium chloride and aluminum chloride. Other disclosed salts include antimony chloride, cobalt chloride, ferric chloride, antimony sulfate, cadmium sulfate and magnesium chloride. The specific examples include as salts calcium chloride, aluminum sulfate and magnesium chloride.
In U.S. Pat. No. 2,342,861, the examples illustrate the addition of a lead soap, specifically lead oleate or naphthenate, to asphalt cutbacks or emulsions to increase their adhesivity for aggregate. Although in all illustrated examples only lead is disclosed as a metal soap to increase adhesivity, that patent suggests that other heavy metal salts of organic acids could be employed including the following metals: Fe, Al, Mn, Zn, Co, Ni, Sn, Ca, Sr, Ba, and Mg. The patent discloses a technique of forming the lead soap by heating a lead oxide in the presence of the desired organic acids. Such lead soaps are then added to the desired asphalt.
Heavy metal salts of high molecular weight organic acids, such as naphthenates or linoleates, have been employed to prevent cracking in blown or oxidized asphalt coatings. For example, U.S. Pat. No. 2,282,703 discloses the use of heavy metals such as cobalt, manganese, iron, lead, vanadium, or zinc dispersed into the blown asphalt for this purpose.
Heavy metal soaps have also been disclosed for use as a dispersant in roofing asphalts to prevent failure of the asphalt due to "alligatoring". U.S. Pat. No. 2,928,753 discloses the polyvalent metal salts of copper, cobalt, or manganese in combination with high molecular weight monocarboxylic acids such as oleic or naphthenic acid. The final disclosed product is an aggregate-free 0.025 inch thick coating on an aluminum sheet so that leveling occurs.
In U.S. Pat. No. 1,505,880, copper slag is added with the aggregate to asphalt to increase the toughness of the resulting pavement composition.
In British Pat. No. 533,977, lead or iron double salts of organic acids are disclosed for the purpose of improving adhesivity of asphalt for mineral aggregate. Also disclosed for this purpose are other di- and and multi-valent metals such as aluminum, chromium, copper and mercury.
In U.S. Pat. No. 4,244,747, as asphalt paving composition is disclosed in which manganese chloride is dissolved in asphalt cement and then mixed with an aggregate. When the manganese chloride is present in quantities of about 0.02 to about 2 weight percent of the asphalt cement, the compressive, flexural and fatigue strength of the ultimate cured paved road is increased.
In U.S. Pat. No. 4,234,346, the use of organic-manganese compounds soluble in asphalt cement are disclosed. Certain organic-manganese compounds, either alone or in cooperation with organic-copper or organic-cobalt compounds, are dissolved in asphalt cement and then mixed with an aggregate to form a paving composition exhibiting increased compressive, flexural and fatigue strength in the ultimate cured pavement.
French Pat. No. 1,567,671 and Austrain Pat. No. 285,788, describe a process for decreasing the content of asphalt paraffins in distillation asphalts, wherein the starting asphalt, in the presence of 0.1 to 1.0 percent manganese or cobalt compounds, is blown with air at a temperature of 110.degree. to 150.degree. C. The asphalt is thus subjected to a catalytic oxidation wherein, besides insoluble metal oxides, such as manganese oxide, a certain portion of soluble metal compounds, such as manganese stearate, are present.